1. Field of the Invention
The present invention relates to an electronically controlled mechanical timepiece which is operated by a mechanical energy storing means, such as a mainspring, serving as a drive source, converts a part of mechanical energy into electrical energy by a power generator, and operates a rotation control means by the electrical power so as to control the rotational cycle. More particularly, the present invention relates to an improvement in the peripheral structure of a power generator for converting mechanical energy into electrical energy.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 8-5758 discloses an electronically controlled mechanical timepiece in which mechanical energy generated when a mainspring unwinds is converted into electrical energy by a power generator, the value of current passing through a coil of the power generator, or the like, is controlled by operating a rotation control means by the electrical energy, and a pointer fixed to a gear train is thereby precisely driven so as to indicate the exact time.
FIGS. 17 and 18 are a plan view and a cross-sectional view, respectively, of a timepiece disclosed in the publication.
Referring to the figures, rotational power from a barrel drum 1 with a mainspring built therein is transmitted to a power generator 20 at an increased speed via a gear train consisting of a center wheel and pinion 7, a third wheel and pinion 8, a fourth wheel and pinion 9, a fifth wheel and pinion 10, and a sixth wheel and pinion 11 supported by a main plate 2, a train wheel bridge 3, and a second bridge 113.
The power generator 20 has a structure similar to that of a step motor for driving a conventional battery-driven electronic timepiece, and comprises a rotor 12, a stator 150, and a coil block 160.
In the rotor 12, a rotor magnet 12b and a rotor inertia disk 12c are formed integrally with the shaft of a rotor pinion 12a that rotates in connection with the sixth wheel and pinion 11.
The stator 150 is formed by winding a stator coil 150b with 40,000 turns around a stator member 150a. 
The coil block 160 is formed by winding a coil 160b with 110,000 turns around a magnetic core 160a. The stator coil 150b and the coil 160b are connected in series so as to output the sum of voltages generated thereby.
In the power generator 20, electrical power obtained by rotation of the rotor 12 is supplied to an electronic circuit having a quartz oscillator via a capacitor (not shown), and the electronic circuit transmits signals for controlling the rotation of the rotor to the coil in accordance with the detected rotation of the rotor and the reference frequency. As a result, the gear train constantly rotates at a constant rotation speed in accordance with the braking force.
Since pointers are driven by the mainspring serving as a power source in such an electronically controlled mechanical timepiece, a motor for driving the pointers is unnecessary and the number of components is small, which lowers the costs. In addition, only a small amount of electrical energy needs to be generated so as to operate the electronic circuit, and the timepiece can be operated by a small amount of input energy.
In the electronically controlled mechanical timepiece described in the above publication, the rotor 12 must be rotated at a constant speed by the force which is generated by the unwinding of the mainspring, and the rotor inertia disk 12c is provided to stabilize the rotation of the rotor 12.
However, since the main plate 2 and the stator 150 are placed around the rotor inertia disk 12c so as to closely face the rotor inertia disk 12c in the axial direction, when the gap between the rotor inertia disk 12c and the main plate 2 or the stator 150 is too small, air viscosity resistance produced therebetween has an adverse effect on the rotation of the rotor 12. That is, when the gap between the components is too small, air viscosity resistance increases and a load torque needed to rotate the rotor 12 also increases. As a result, the period of operation of the timepiece is shortened in accordance with the increase.
As the power generator used in the electronically controlled mechanical timepiece, a power generator having a structure similar to that of a brushless motor is sometimes used, besides the power generator including the inertia disk 12c. In such a power generator, a pair of disk-like stator members are mounted along the axial direction of the rotor, and are provided with a plurality of magnets arranged in the circumferential direction so that the poles thereof are alternately different. A coil formed on a substrate is interposed between these stator members (between the magnets). Accordingly, since the rotor itself including the disk-like stator members also functions as an inertia disk, the above-described inertia disk 12c is unnecessary.
In such a power generator, however, when the gap between the stators, and the main plate or the coil is too small, the above problems are also caused by air viscosity resistance between the components.
An object of the present invention is to provide an electronically controlled mechanical timepiece in which the period of operation thereof can be extended by reducing the influence of air viscosity resistance.
According to the present invention, there is provided an electronically controlled mechanical timepiece wherein a mechanical energy transmitting means is driven by a mechanical energy storing means serving as an energy source, electrical power is generated by a power generator rotated by the mechanical energy transmitting means, the rotation cycle of the power generator is controlled by an electronic circuit driven by the electrical power so as to brake the mechanical energy transmitting means and to thereby adjust the speed, characterized in that the power generator has a rotor rotating in connection with the mechanical energy transmitting means, and a constant K is set to be {fraction (1/10)} or less when a gap h between a largest-diameter member in the rotor and a counter component fixed to most closely face the rotor in the axial direction is given by the following formula:   h  =                              π          2                ⁢        f        ⁢                  xe2x80x83                ⁢        μ                    K        ⁢                  xe2x80x83                ⁢                  T                      rz            ⁢                          xe2x80x83                        ⁢            max                                ⁢          (                        r          2          4                -                  r          1          4                    )      
where xcfx80 represents the ratio of the circumference of a circle to its diameter, xcexc represents the air viscosity, f represents the rotational frequency of the rotor, Trzmax represents the maximum output torque of the mechanical energy storing means to be transmitted to the rotor, r1 represents a distance from the center of rotation of the rotor to the inner periphery of a portion where the largest-diameter member in the rotor and the counter component overlap in a plane, and r2 represents a distance from the center of rotation of the rotor to the outer periphery of the portion where the largest-diameter member in the rotor and the counter component overlap in a plane.
Herein, xe2x80x9ccounter componentxe2x80x9d and xe2x80x9clargest-diameter memberxe2x80x9d refer to a component and a member between which viscosity resistance increases as the gap h therebetween decreases, thereby increasing the load torque at the rotor.
Therefore, xe2x80x9ccounter componentxe2x80x9d does not include a component, for example, a bridge-shaped or cantilevered supporting member claimed as in the following, which overlaps with the largest-diameter in the rotor in a plane and in which air viscosity resistance between the component and the largest-diameter member does not cause any problem even when the gap h decreases.
Regarding xe2x80x9clargest-diameter memberxe2x80x9d, for example, in a case in which a projection for enhancing inertia is formed at a position on the largest-diameter member, such as a rotor inertia disk, offset outward from the midpoint of the radius of the largest-diameter member so as to protrude toward the counter component, when the area of a portion of the projection, which overlaps with the counter component in a plane, is less than ⅕ of the area formed by the largest diameter, air viscosity resistance between the opposing surfaces of the projection and the counter component does not cause a problem. Such a gap between the opposing surfaces does not correspond to the gap h of this invention. The gap h of this invention refers to a gap between a surface of a component other than the projection and the counter component. The projection does not correspond to the largest-diameter member of this invention.
Even if the above projection is provided offset from the midpoint of the radius of the largest-diameter member, such as a rotor inertia disk, toward the center, when the area of a portion of the projection overlapping with the counter component in a plane is less than ⅖ of the area formed by the largest diameter, air viscosity resistance between the opposing surfaces of the projection and the counter component does not cause a problem. Such a gap between the opposing surfaces also does not correspond to the gap h of this invention. The gap h of this invention refers to a gap between the surface of a component other than the projection and the counter component. The projection also does not correspond to the largest-diameter member of this invention.
In the present invention described above, while the power generator is structured to include the rotor, the gap h between the largest-diameter member in the rotor, where air viscosity resistance is prone to cause a problem, and the counter component, is set so that the load torque due to air viscosity resistance between the components is equal to or less than 1/10 (10%) of the maximum output torque Trzmax to be transmitted from the mechanical energy storing means to the rotor.
For example, a graph shown in FIG. 14 shows the relationship between the load torques T2# at the center wheel and pinion 7 (see FIGS. 1 and 2 for the reference numeral) which the present inventor obtained by conducting an experiment described in a first example, which will be described later, and the gap h, and the relationship between values obtained by converting the rotor load torques Trz due to air viscosity, which the present inventor calculated according to the theory described in a first embodiment, which will be described later, into load torques T2# at the center wheel and pinion 7.
Referring to this graph, since the values obtained by subtracting calculated values from actually measured values are substantially constant regardless of the gap h, it can be determined that these values are load resistances other than air viscosity resistance acting between a rotor 12 and the counter component (for example, stators 123 and 133), such as mechanical friction in the gear train and viscosity resistance of oil at a tenon.
In contrast, a graph shown in FIG. 16 shows the relationship among the gap h, the period of operation, and the thickness of the movement, as described in a second example which will be described later.
It is known from the graphs shown in FIGS. 14 and 16 that the load due to air viscosity rapidly increases and the period of operation is rapidly shortened when the gap h is less than 0.1 mm. The period of operation is determined by the relationship between the ability of a mainspring 1a and a load torque necessary for driving the timepiece. The load torque Trz at the rotor 12 due to air viscosity when the gap h is 0.1 mm is 84.34xc3x9710xe2x88x926 Nxc2x7m (a value obtained by converting 0.86 gcm into the International System of Units) which is converted into the load torque at the center wheel and pinion 7, as shown in the graph in FIG. 14. This load torque corresponds to nearly 1/10 of the maximum output torque Trzmax to be transmitted from the mainspring 1a serving as the mechanical energy storing means to the rotor 12.
From the above, when the gap h is set so that the coefficient K is 1/10 or less, the load torque Trz at the rotor 12 due to air viscosity resistance is limited, and energy loss in the mechanical energy storing means is also limited, which extends the period of operation of the timepiece.
An electronically controlled mechanical timepiece claimed as in Claim 2 is characterized in that the coefficient K is set to be 1/20 to 1/60.
An electronically controlled mechanical timepiece claimed as in Claim 3 is characterized in that the coefficient K is set to be 1/20 to 1/40.
FIG. 16 shows that the period of operation is not extended while the thickness of the movement increases when the gap h is 0.6 mm or more. When the gap h is 0.6 mm, the converted load torque T2xc2x7 at the center wheel and pinion 7 due to air viscosity is 13.73xc3x9710xe2x88x926 Nxc2x7m (a value obtained by converting 0.14 gcm into the International System of Units), as shown in FIG. 14, and it corresponds to nearly 1/60 of the maximum output torque Trzmax to be transmitted from the mainspring 1a to the rotor 12.
In consideration of the period of operation and the thickness of the movement required for the timepiece, a more preferable gap h is approximately 0.2 mm to 0.4 mm. The load torque T2# due to air viscosity is 42.17xc3x9710xe2x88x926 Nxc2x7m (a value obtained by converting 0.43 gcm into the International System of Units) when the gap h is 0.2 mm, and is 21.57xc3x9710xe2x88x926 Nxc2x7m (a value obtained by converting 0.22 gcm into the International System of Units) when the gap h is 0.4 mm, which respectively correspond to nearly 1/20 and 1/40 of the maximum output torque Trzmax to be transmitted from the mainspring 1a to the rotor 12.
An electronically controlled mechanical timepiece is characterized in that the counter component is a supporting member for supporting at least one end portion of the rotor in the axial direction, and in that the supporting member is disposed at a greater distance in the axial direction from the rotor than a bearing held by the supporting member so as to receive the one end in the axial direction.
As the supporting member, for example, a train wheel bridge for receiving a gear train serving as the mechanical energy transmitting means, and a main plate may be adopted.
In such a configuration, the supporting member, which is disposed at a greater distance (at a greater distance in the radial direction) from the center of rotation of the rotor than the bearing close to the center of rotation, is also at a greater distance from the rotor in the axial direction. This makes it possible to reliably ensure the gap h between the supporting member and the largest-diameter member in the rotor while appropriately maintaining the engaged state between the bearing and the rotor in the axial direction without any change.
An electronically controlled mechanical timepiece is also characterized in that the counter component is a supporting member for supporting at least one end portion of the rotor in the axial direction, in that the supporting member includes a holding section for holding a bearing for receiving the one end in the axial direction, and in that a portion on the periphery of the holding section is disposed at a greater distance from the rotor in the axial direction than the holding section. As the supporting member, a gear train and a main plate may also be adopted.
In such a configuration, since only the portion of the supporting member closely facing the largest-diameter member in the rotor is at a great distance from the rotor, and the structure and the like of the bearing itself are not changed, the same operations and advantages as those described above are provided. In addition, since the holding section formed in the supporting member so as to hold the bearing is not at a great distance from the rotor and is made to be sufficiently thick, the bearing is thereby held reliably. In this case, since the holding section is placed offset toward the center of rotation of the rotor, that is, at a position where the peripheral velocity of the rotor is low and air viscosity resistance is not serious, it does not act to shorten the period of operation of the timepiece.
An electronically controlled mechanical timepiece is further characterized in that one end portion of the rotor in the axial direction is supported by a supporting member which is formed separately from a component for supporting the mechanical energy transmitting means and which is shaped like a bridge or is cantilevered.
In such a configuration, since the supporting member for supporting the rotor is formed separately from the component for supporting the mechanical energy transmitting means, the rotor supporting member can be bridge-shaped or be cantilevered, not in the form of planar surfaces, but in ae form nearly like a rod. Therefore, it is possible to reliably place the counter component, closely facing the rotor in the axial direction, at a distance larger than the gap h while reliably supporting the rotor.
An electronically controlled mechanical timepiece is also characterized in that the mechanical energy transmitting means is a gear train including a plurality of wheels, and in that a gap hxe2x80x2 in the axial direction between the rotor and the wheels serving as the mechanical energy transmitting means to be meshed with the rotor is smaller than the gap h.
In such a case, the thickness of the timepiece is reduced by setting the gap hxe2x80x2 to be smaller than the gap h, which further reduces the thickness of the timepiece. In this case, since the portions of the wheels and the rotor (a rotor inertia disk or a rotor member which will be described later) overlapping with each other move in the same direction with the rotation in the engaged state, the relative speed at the overlapping portions is not very high. There is no problem in practice as long as the gap h is set so that the wheels meshed with the rotor and the rotor do not contact even when they undergo runout due to air viscosity resistance produced between the components. When hxe2x80x2xe2x89xa71/2 h, the influence of air viscosity resistance can be reduced sufficiently.
An electronically controlled mechanical timepiece is characterized in that a proximity component is interposed between the largest-diameter member in the rotor and the counter component, and in that the proximity component has a through opening extending in the axial direction at a position corresponding to the largest-diameter member of the rotor.
In such a configuration, since the opening is formed at the position of the proximity component facing the largest-diameter member in the rotor, it is possible to place the proximity component between the largest-diameter member in the rotor and the counter component without any influence on the load torque of the rotor while reliably ensuring the gap h between the largest-diameter member and the counter component, and to thereby enhance the efficiency of layout in a component layout space inside the timepiece.
An electronically controlled mechanical timepiece is characterized in that the pressure inside a movement including the mechanical energy storing means, the mechanical energy transmitting means, and the power generator, is reduced.
Herein, xe2x80x9cthe pressure is reducedxe2x80x9d includes a vacuum state.
In this invention, since the air density inside the movement is low, air viscosity resistance described above does not cause a problem, and the period of operation of the timepiece can be extended substantially.
On the other hand, an electronically controlled mechanical timepiece is also characterized in that the rotor in the power generator has an inertia wheel protruding in the radial direction, and in that the inertia wheel serves as the largest-diameter member in the rotor.
An electronically controlled mechanical timepiece is characterized in that the rotor in the power generator has a rotor member protruding in the radial direction and having a plurality of rotor magnets arranged in the circumferential direction, and in that the rotor member serves as the largest-diameter member in the rotor.
As such power generator used in the electronically controlled mechanical timepiece of this invention, two types of power generators, a type including a rotor with an inertia wheel and a type including a rotor having a rotor member, may be adopted.